feat(agent-html): add Text primitive component and support

This commit adds the Text primitive component to the agent-html DSL, including:
- Add Text tag to all tag sets and UI tag union type
- Add variant prop support for Text component
- Add validation to block element children inside Text nodes
- Create test fixtures and tests for basic Text usage
- Update example dashboard to use new Text components
- Refactor example shell to use dialog for source view

Author: Sayhi-bzb

.agents/skills/agent-html/references/examples.md

@@ -13,14 +13,20 @@ Use the closest valid fixture before inventing new structure.
 - `card-tabs-grid.xml`
 - `complex-dashboard.xml`
 - `icon-basic.xml`
+- `image-basic.xml`
 - `minimal-page.xml`
+- `text-basic.xml`
 
 ## Invalid Patterns
 
 - `bare-text-under-grid.xml`
 - `carousel-missing-content.xml`
 - `chart-missing-series.xml`
+- `image-invalid-fit.xml`
+- `image-invalid-src.xml`
+- `image-with-child.xml`
 - `layout-gap-not-allowed.xml`
 - `missing-tabs-trigger-value.xml`
+- `text-with-child.xml`
 - `unknown-icon-name.xml`
 - `unknown-tag.xml`

.agents/skills/agent-html/references/grammar.md

@@ -85,12 +85,16 @@
 - `ChartTooltip:hideLabel?="true|false" -> none`
 
 - `Icon:name=string -> none`
+- `Image:src=string, alt=string, fit?="cover|contain" -> none`
+- `Text:variant?="h1|h2|h3|h4|p|lead|large|small|muted|inline-code" -> Text`
 
 ## Canonical Example
 
 ```xml
 <Page title="Gallery Preview">
   <Stack>
+    <Text variant="muted">Use Text for standalone copy inside layout nodes.</Text>
+
     <Card>
       <CardHeader>
         <CardTitle>Controls</CardTitle>